The invention is directed to a HF-excited, diffusion-cooled stripline laser having a grounding electrode and a HF metal electrode arranged thereabove which are provided with means for mutual fixing. Respective cooling channels are provided and between which a discharge gap is formed. Parallel inductances are attached to the electrodes and are uniformly distributed over their length. An unstable resonator is provided. An electrically conductive, vacuum-tight housing containing a CO.sub.2 lasing gas surrounds the resonator and the electrodes and is composed of a first and a second face plate and of a cylindrical outside wall connected thereto.
Apart from the parallel inductances, such a stripline laser is disclosed by EP-A-0 477 865. Parallel inductances, but only for waveguide lasers, are disclosed by U.S. Pat. No. 4,352, 188.
Until a few years ago, insurmountable difficulties opposed the design of a CO.sub.2 high-power laser in a compact structure. Due to the physical processes in the laser excitation, the efficiency is highly dependent on a gas temperature that is not excessively high, i.e., on an effective elimination of excess heat from the laser gas in practice. Given diffusion-cooled CO.sub.2 lasers, wherein the heat is conveyed by a stationary thermal conduction process from the hottest location in the center of the laser plasma to the cooled walls of the discharge vessel, it has been shown that the laser output power is only dependent on the length and not on the diameter of the discharge. As a result, complicated convolution designs were therefore developed on the one hand in order to retain compact dimensions of the laser, despite powers up into the kW range. On the other hand, rapidly flowed, i.e. convection-cooled lasers, were developed. Rapidly flowed lasers of the power class 500 up to more than 10,000 W are currently commercially obtainable. These lasers, which are not provided for sealed-off operation, however, are bulky, have a high power-associated weight, and are dependent on a cost-unfavorable, external gas supply and on pumping for rapid gas circulation.
For the stated reasons, only what are referred to as waveguide lasers having powers up to 200 W were previously obtainable as compact, diffusion-cooled CO.sub.2 lasers. In the meantime, however, the fundamentals of a stripline laser have been disclosed, for example by EP-A-0 305 893, the discharge space thereof--by contrast to the waveguide laser--not having a quadratic cross section but being based on planar waveguide structures that are open toward the side. The combination of such a quasi-one-dimensional waveguide with an unstable resonator in the orthogonal direction thereby enables a diffraction-limited, fundamental mode laser emission. Given this stripline design, the heat is absorbed in large-area fashion by the closely neighboring electrodes, and is then eliminated therefrom with the assistance of suitable coolants. It is therefore no longer necessary to pump the laser gas itself through the discharge space with a special cooling circulation.
The article by R. Vowack et al, "Diffusionsgekuehlte CO.sub.2 Hochleistungslaser in Kompaktbauweise" in "Laser und Optoelektronik", 23(3)/1991 is referenced to the prior art of stripline lasers. Up to now, considerable difficulties still oppose the conversion of the above-described stripline laser concept into a structure compatible with practice. The selection of a suitable electrode material proved especially problematical. The electrodes serve, on the one hand, for coupling in the high-frequency energy, i.e. are loaded with high currents. Moreover, they should form an optimally loss-free optical waveguide and eliminate the heat well. Over and above this, only component parts and materials are suitable with which an equilibrium condition of the gas mixture in the laser that is stable over the long term is guaranteed. In the article, for example, the anticipated, undesirably high CO.sub.2 decomposition due to copper electrodes is discussed. Further demands made of the construction of cooled electrodes provided with means for mutual distancing are the optimization of the weight, adequate stability with respect to mechanical or thermal stresses and, last but not least, cost-beneficial manufacturability.
For resolving these and other problems, the European application bearing Ser. No. 92114862.3, which does not enjoy prior publication, proposed that each electrode is designed as a composite composed of a carrier part having a mechanically stable profile and a plate-shaped electrode part with integrated cooling that faces toward the discharge gap and is hard-soldered or welded to the carrier part. The carrier part should thereby preferably comprise an approximately rectangular cross section. In this design, however, the problem of the HF voltage distribution between the two electrodes arranged above one another and the cylindrical outside wall that surrounds them, which simultaneously serves as HF shielding and as an outer conductor, is not yet resolved in a completely satisfactory fashion. These problems arise despite parallel inductances since, differing from waveguide lasers, the grounding electrodes and the outside wall are not identical for thermal reasons.